The present invention relates to an automatic focus controlling apparatus and method for use in an image pick-up apparatus comprising a two-dimensional solid state image sensing device upon which an image of an object is focused by an imaging lens.
Heretofore, there has been proposed automatic focus controlling apparatus and method for use in a television camera or a still camera, wherein an image of an object is automatically focused onto a light receiving surface of an image sensing device or a film surface by means of a photography lens. For example, in the television camera, a part of the light flux transmitted through the photography lens is detected by light receiving elements positioned at conjugate points with respect to a light receiving surface of an image pick-up tube so as to derive a focusing error signal in accordance with a defocused condition of a projected image. Then, the photography lens is moved in an optical axis direction by energizing a motor in relation to the focusing error signal, and thus the image can be always formed on the light receiving surface of the image pick-up tube in an in-focused condition. There has been also proposed a still camera in which the in-focused image can be formed on the film surface by driving the photography lens in accordance with the detected focusing error signal. However, in the known image pick-up apparatuses mentioned above, since the large and heavy photography lens must be moved in the optical axis direction by energizing the motor, a driving system becomes large and it is very difficult to move the photography lens at a high speed. In the television camera, since the photography lens becomes especially large in size and heavy in weight, it is not possible to perform the fast focus controlling operation.
Currently, according to a development in a semiconductor field, there has been developed a television camera using a two-dimensional solid state image sensing device such as CCD or BBD, and further proposed a still camera using such a solid state image sensing device.